imerge: fix ancestor calculation

If wctx already has two parents, ancestor calculation is wrong.
Normally merge is called before wctx gets the second parent, so
we simulate this in imerge by temporarily popping the second parent
before calling filemerge. Highly dirty.

This patch also handles the ParseError move from cmdutil to dispatch.

hgext/imerge.py

@@ -7,7 +7,7 b' imerge - interactive merge'
 
 from mercurial.i18n import _
 from mercurial.node import *
-from mercurial import commands, cmdutil, fancyopts, hg, merge, util
+from mercurial import commands, cmdutil, dispatch, fancyopts, hg, merge, util
 import os, tarfile
 
 class InvalidStateFileException(Exception): pass
@@ -113,8 +113,15 b' class Imerge(object):'
         wlock = self.repo.wlock()
 
         (fd, fo) = self.conflicts[fn]
-        p2 = self.wctx.parents()[1]
-        return merge.filemerge(self.repo, fn, fd, fo, self.wctx, p2)
+        p1, p2 = self.wctx.parents()
+        # The filemerge ancestor algorithm does not work if self.wctx
+        # already has two parents (in normal merge it doesn't yet). But
+        # this is very dirty.
+        self.wctx._parents.pop()
+        try:
+            return merge.filemerge(self.repo, fn, fd, fo, self.wctx, p2)
+        finally:
+            self.wctx._parents.append(p2)
 
     def start(self, rev=None):
         _filemerge = merge.filemerge
@@ -269,7 +276,7 b' subcmdtable = {'
     'unresolve': (unresolve, [])
 }
 
-def dispatch(im, args, opts):
+def dispatch_(im, args, opts):
     def complete(s, choices):
         candidates = []
         for choice in choices:
@@ -292,9 +299,9 b' def dispatch(im, args, opts):'
         args = fancyopts.fancyopts(args, optlist, opts)
         return func(im, *args, **opts)
     except fancyopts.getopt.GetoptError, inst:
-        raise cmdutil.ParseError('imerge', '%s: %s' % (cmd, inst))
+        raise dispatch.ParseError('imerge', '%s: %s' % (cmd, inst))
     except TypeError:
-        raise cmdutil.ParseError('imerge', _('%s: invalid arguments') % cmd)
+        raise dispatch.ParseError('imerge', _('%s: invalid arguments') % cmd)
 
 def imerge(ui, repo, *args, **opts):
     '''interactive merge
@@ -317,6 +324,10 b' def imerge(ui, repo, *args, **opts):'
 
     status:
       show the current state of the merge
+      options:
+        -n --no-status:  do not print the status prefix
+           --resolved:   only print resolved conflicts
+           --unresolved: only print unresolved conflicts
     next:
       show the next unresolved file merge
     merge [<file>]:
@@ -353,7 +364,7 b' def imerge(ui, repo, *args, **opts):'
     if not args:
         args = ['merge']
 
-    return dispatch(im, args, opts)
+    return dispatch_(im, args, opts)
 
 cmdtable = {
     '^imerge':